Raining on the animal parade

Half of the mammals, birds, amphibians and reptiles living in Colorado’s mountains are at risk of becoming extinct over the next century, according to a recent paper co-authored by a University of Colorado professor.

Climate change predictions that calculate only for temperature changes estimate extinction risks of about 5 percent of species. In this study, which looks at temperature increase and precipitation changes for 16,848 vertebrate species on 156 mountains, the possible local extinction rate increases 10-fold to roughly 50 percent over the next 100 years.

“Everyone thinks about just temperature change, but the truth is that for vertebrates and other mountain organisms, what these models are showing is that precipitation change can be so much more severe,” says Christy McCain, assistant professor in the University of Colorado’s Department of Ecology and Evolutionary Biology and curator of vertebrates for the CU Museum of Natural History. McCain co-authored the paper with University of Connecticut professor Robert Colwell.

Most climate change models don’t predict what the effect will be on precipitation, a more expensive and more tricky variable to calculate.

“So we said, let’s run the models for wetter, drier and average and see how species might respond,” McCain says. “How much of their niche that they have now would be there in 100 years under all three of those scenarios?” The expectation is that animals will move up in elevations to stay in cooler temperatures. Only a few of them, a few specialist species that live at the tops of peaks, would need to essentially float off the mountain to stay in cool enough temperatures.

In temperate climates, higher elevations tend to be wetter, meaning desert species could find themselves tracking their ideal temperatures into much wetter climates, McCain says. And at higher elevations, much of the precipitation falls in the form of snowpack, when many of the native species are dormant and unable to access it.

“Wewere just trying in our models to say, OK, there is uncertainty around how precipitation is going to change, but if we look at all that uncertainty, what is the risk?” McCain says. They ran their models assuming various levels of adaptability to wetter or drier climates for species. “Regardless of which model you use … the risks are so much higher because of this disconnect between tracking a cooler temperature and moving outside your precipitation that you’re used to having.”

In Central America, where drastically drier conditions are predicted for the next century, amphibians like salamanders and frogs face a local extinction risk of up to 91 percent and 71 percent, respectively. In the Rockies, even common species like certain chipmunks and shrews are at risk, as is the more isolated American pika. North American local extinction risks go as high as 49 percent of vertebrate species per mountain range.

Research from a CU-Boulder study team on pikas in the southern Rocky Mountains has shown pika populations abandoning drier sites.

“We suspect that a lack of snowpack leads to a lack of insulation for pikas in the winter. … If they’re exposed to cold temperatures, because there isn’t sufficient snowpack, they could potentially freeze to death,” says Liesl Erb, the doctoral student who led the study team that assessed historic sites for pikas. “It’s also possible that the lack of precipitation could lead to lack of sufficient water in the vegetation that they eat. At this point it could be a combination of those factors.”

John Williams, a professor at the University of Wisconsin, has also studied climate change models that factored for both precipitation and temperature.

“What we found was that these climate model projections for the 21st century, if you compare those projections to the late 20th climates, you see areas where there’s novel climates emerging and current climates disappearing,” he says. “Meaning that in some areas of the world, climates that exist today will disappear or greatly shrink in size by the end of the century. In other areas of the world, mainly in the lower tropics, there will be expansions or appearances of novel climates that have not been seen within the earth’s system over the last several million years.”

These new climates might expand the habitat for some species, like those that live in relatively warm environments, but it could also eliminate the environments of those that prefer relatively cold environments, Williams says.

“There is some question of surprise,” he says. “What will happen in these novel climates that are outside of our experience?”